1. Field of the Invention
The present invention relates to an improved process or method for transferring at least one coating or laminating a coated or uncoated film onto at least one geometrically defined surface of a lens substrate, which can be implemented in a short period of time without any risk of deformation of the lens substrate, and results in the coating or the coated or uncoated film adhering to the lens substrate through an adhesive layer of uniform thickness.
Furthermore, the process or method of the invention allows transferring a coating or laminating a coated or uncoated film on a rough surface of a lens substrate, i.e. a surface of a lens substrate that has been surfaced and fined but not polished or a surface which has been surfaced (cut) (typically by digital surfacing) and not polished.
2. Description of Related Art
It is a common practice in the art to coat at least one main surface of a lens substrate, such as an ophthalmic lens or lens blank, with several coatings for imparting to the finished lens additional or improved optical or mechanical properties. These coatings are designated in general as functional coatings.
Thus, it is usual practice to coat at least one main surface of a lens substrate, typically made of an organic glass material, with successively, starting from the surface of the lens substrate, an impact-resistant coating (impact resistant primer), an abrasion- and/or scratch-resistant coating (hard coat), an anti-reflection coating and, optionally, an anti-fouling top coat. Other coatings such as a polarized coating, a photochromic or a dyeing coating may also be applied onto one or both surfaces of the lens substrate.
Numerous processes and methods have been proposed for coating a surface of an ophthalmic lens and are disclosed.
U.S. Pat. No. 6,562,466 describes one process or method for transferring a coating from at least one mold part onto at least a geometrically defined surface of a lens blank comprising:                providing a lens blank having at least one geometrically defined surface;        providing a support or mold part having an internal surface bearing a coating and an external surface;        depositing on said geometrically defined surface of said lens blank or on said coating a pre-measured amount of a curable adhesive composition;        moving relatively to each other the lens blank and the support to either bring the coating into contact with curable adhesive composition or bring the curable adhesive composition into contact with the geometrically defined surface of the lens blank;        applying a sufficient pressure onto the external surface of the support so that the thickness of a final adhesive layer once the curable composition cured is less than 100 micrometers;        curing the layer of adhesive composition; and        withdrawing the support or mold part to recover the lens blank with the coating adhered onto the geometrically defined surface of said lens blank.        
U.S. Pat. No. 6,562,466 uses a liquid light or thermal curable adhesive composition to transfer the coating layers from the carrier to the surface of the lens substrate. The liquid curable adhesive composition is required to stick both to the exposed coating on the carrier and the geometrically defined surface of the lens substrate. The process requires to precisely dropping the liquid adhesive composition, either too much or too less of the liquid adhesive needs to be avoided, which renders the process more complicated and less cost effective. Furthermore, this process may cause optical distortions when the liquid adhesive composition is not spread out very evenly on the lens curved surface, especially when the lens surface has multiple curves. In particular, when the liquid adhesive composition is spread using air pressure (inflatable membrane apparatus) applied on a flexible coating carrier, the applied pressure may not usually be uniform over the whole carrier surface, resulting in an uneven spreading of the liquid adhesive composition and a final cured adhesive layer having some variations in thickness.
Published US patent application no 2006-0219347 discloses a process or method for transferring at least one coating from a carrier onto a geometrically defined surface of a lens substrate which comprises the steps of:                (a) obtaining a carrier having a main surface bearing at least one functional coating;        (b) obtaining a lens substrate having at least one geometrically defined surface;        (c) depositing, either on said at least one functional coating or said at least one geometrically defined surface of the lens substrate, a layer of an adhesive composition;        (d) bringing said layer of adhesive composition to a state at which the layer becomes unflowable under the process conditions if said layer is not already in such a state at the end of step (c);        (e) moving the carrier and the lens substrate relatively to each other to bring the layer of the adhesive composition into direct contact with either said at least one geometrically defined surface of the lens substrate or said at least one functional coating;        (f) pressing together the layer of the adhesive composition and either said at least one functional coating or said at least one geometrically defined surface of the lens substrate;        (g) optionally, applying heat during pressing step (f);        (h) stopping pressing step (f); and        (i) withdrawing the carrier to recover the lens substrate coated with said at least one functional coating adhering to said at least one geometrically defined surface through the layer of transparent adhesive composition.        
The adhesive composition is selected from the group consisting of pressure-sensitive adhesives (PSA) and hot-melt adhesives (HMA).
Nevertheless, there is still a need for a better control of the thickness of the adhesive layer and minimizing the thickness variation of the adhesive layer on the entire substrate surface. There is also still a need of a better covering of a lens substrate rough surface, i.e. a surface that has been surfaced and fined, but not polished, by the adhesive layer, the adhesive material filling up the surface irregularities or a lens substrate that has been surfaced by digital surfacing but not polished.
Besides, there is also a need to improve final product performance, such as thermal resistance.
U.S. Pat. No. 5,128,388 discloses a hot melt adhesive (HMA) crosslinkable by UV irradiation comprising a hot melt adhesive base, a saturated hydrocarbon oligomer containing at least on acryloyl group in a molecule for affording crosslinkability by ultraviolet irradiation, and a photopolymerization initiator. The HMA base is a block thermoplastic elastomer comprising polystyrene blocks and polybutadiene, or polyisoprene or ethylene-butylene copolymer blocks.
U.S. Pat. No. 5,128,388 also discloses a process for preparing an optical disc which comprises applying the UV crosslinkable HMA on one of a pair of substrates, irradiating with UV radiation the applied HMA, and then putting the other substrate onto the surface of HMA.